1. Field of the Invention
The present invention relates to a seismic isolation apparatus. More particularly, the present invention relates to a seismic isolation apparatus advantageously used for single family houses having a light weight.
2. Description of the Related Art
For protection of buildings from earthquake, seismic isolation apparatus in which a plurality of hard plates having rigidity such as steel plates and a plurality of soft plates having viscoelastic property such as rubber plates are arranged to form alternating layers have heretofore been used. It is generally practiced that, by shifting the proper vibration of a building to a lower value by supporting the building with the seismic isolation apparatus to avoid resonance of the building with the quake wave, the building is controlled to have a movement which is low in the frequency although large in the displacement, and that the vibration is damped in a short time by the combined use of a damper. As the damper used in combination with the seismic isolation apparatus, a damper of a rigid metal rod, a friction damper, and a viscous damper are used. A multilayer rubber having a lead plug confined into a composite multilayer structure and a high damping laminated rubber using a rubber having a high damping property are also used.
In recent years, seismic isolation of single family houses has been desired in addition to seismic isolation of heavy construction structures such as high rise buildings and bridges. However, when a conventional seismic isolation apparatus for heavy weight (for large buildings) is used as the seismic isolation apparatus for a single family house having a light weight, it is inevitable because of the light weight of the house that the seismic isolation apparatus has a small diameter and a large height in order to obtain the desired seismic isolating property. This shape is not suitable for practical use because buckling takes place very easily.
A rubber having a low elasticity which is suitable for supporting a light weight is necessary for obtaining the seismic isolation effect suitable for a structure having a light weight. However, when a rubber having a low elasticity is used, shake by wind arises because of the low elasticity. It is also strongly desired for a seismic isolation apparatus used for single family houses that the seismic isolation apparatus can isolate small vibrations (traffic vibration).
Thus, it has been desired that a seismic isolation apparatus for single family houses satisfies the following three requirements: (1) seismic isolation, (2) prevention of shake by wind, and (3) isolation of traffic vibration. No seismic isolation apparatus satisfying all these requirements is heretofore known.